Why Would Someone Wear Rubber Gloves to Feed Lambs
Current Therapy in Large Animal Theriogenology. 2007 : 680–695.
Lambing Management and Neonatal Care
Guest Editor (s): ROBERT S. YOUNGQUIST, DVM, Diplomate ACVIM
Professor and Associate Chairman, Department of Veterinary Medicine and Surgery, College of Veterinary Medicine, University of Missouri, Columbia, Missouri
Guest Editor (s): WALTER R. THRELFALL, DVM, MS, PhD, Diplomate ACT
Theriogenology Area, Department of Veterinary Clinical Sciences, College of Veterinary Medicine, The Ohio State University, Columbus, Ohio
PRELAMBING MANAGEMENT OF PREGNANT EWES
Midgestation
Approximately 40 days after the ram is removed from the flock, scanning for pregnancy using real-time ultrasound examination is recommended to identify those animals that are not pregnant. To improve nutritional management of late-gestation ewes, fetal number also should be determined and ewes classified by body condition score.
Pregnant ewes can be grouped for feeding as follows:
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Ewes with singles in good condition
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Ewes with twins in good condition and ewes with singles in poor condition
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Ewes with triplets or more and ewes with twins in poor condition
One Month before First Expected Lambing Date
The following management procedures should be performed routinely approximately 1 month before lambing:
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Ewes should receive "booster" immunization with a multiway clostridial vaccine that includes antigens effective against tetanus, pulpy kidney (Clostridium perfringens type D), enterotoxemia (C. perfringens type C), malignant edema (Clostridium chauvoei and Clostridium septicum), and Black's disease (Clostridium novyi). If the ewes have not had a primary series as lambs, or if the previous vaccination was administered more than 12 months previously, then a primary series should be given starting at 2 months before the first expected lambing date. A vaccine that contains antigens to Corynebacterium pseudotuberculosis (the agent of caseous lymphadenitis) can be included if the disease is present in the flock.
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Shear or, in sheep maintained outdoors in inclement weather, crutch (remove wool from the perineal or escutcheon area) all pregnant ewes. Shearing increases dry matter intake, is associated with improved fetal lamb growth, and improves udder cleanliness for nursing lambs.
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Increase energy and energy density of ration.
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Increase energy to ewes in poor body condition.
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Loose, clean free-choice mineral formulated for sheep, with added salt to increase palatability, should be available at all times. Special attention should be paid to providing adequate calcium if cereal hays are fed; supplemental selenium, cobalt, copper, iodine, and molybdenum if regional soils and forages are known to be deficient; and vitamin E and vitamin A if stored feeds are fed.
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If sheep are bunk fed, feeder space should allow all ewes to eat at once (i.e., a minimum of 40 cm [16 inches] of feeder space per pregnant ewe) (Table 91-1 ).
Table 91-1
Housing Requirements for Ewes and Nursing Lambs
Production Period Animal Class Housing Type Space Numbers Late gestation and lambing Ewes Pen feeder 16 ft2/ewe 20 inches of feeder space/ewe for limit-fed animals, 6 inches for free-choice–fed animals <40 ewes/pen Waterer 25–50 ewes/bowl, 15–25 ewes/foot of tank 1–3 days of age Ewes and lambs Claiming pen 4–5 ft/ewe-lamb pair 12 pens/100 ewes: natural breeding 40 pens/100 ewes: synchronized breeding Lactation Ewes with lambs Pen 20 ft2 per ewe-lamb pair; extra 5 ft2 for prolific breeds 2–4 days old: 5–10 ewes-lambs/pen 5–14 days old: 20–40 ewes-lambs/pen 14 days to weaning: 50–100 ewes-lambs/pen Feeder and waterer as for gestating ewes Nursing and early weaning (<28 days) Lambs Creep area 2 ft2/lamb 2-inches of feeder space/lamb As for nursing lambs; 25/pen for early weaned lambs Data from Canadian Farm Buildings Handbook, Agriculture and Agrifood Canada.
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If sheep are housed in a barn or dry lot, additional space must be allowed for pregnancy (a minimum of 1.4 m2 [16 square feet] per ewe) (see Table 91-1).
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Treatment with an anthelmintic is given to prevent preparturient rise in fecal egg count. This recommendation may be modified according to regional conditions.
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If sheep are shorn or if warranted, treatment for external parasites (lice, keds, and mange) is given.
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For ewes lambing at pasture, supplementation with a coccidiostat in the mineral premix may be helpful to reduce contamination of lambing grounds.
Two Weeks before First Expected Lambing Date
The lambing area is prepared as follows:
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Lambing on pasture: Straw bales are positioned to create a windbreak and to bed lambing grounds. After lambing is finished, straw can be gathered in and burned or composted. Protection against predators (e.g., guard animals) should be ensured.
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Lambing inside: Ventilation must be adequate for animal numbers. Temperature fluctuations where young lambs are to be housed should be avoided. Building or pens should be cleaned out and disinfected and fresh bedding applied to lambing area.
Lambing and lamb processing equipment and medications should be available (Box 91-1 ).
PARTURITION (LAMBING)
Gestation length varies considerably with breed of sheep. It also varies within breed with number of fetuses being carried. Triplet-bearing ewes usually lamb before single-bearing ewes bred on the same day. On average, sheep gestate for 145 days. Normal lambings have been reported as early as day 137, but generally sheep do not lamb earlier than day 142.
At 1 week before the first expected lambing date (day 138 after the ram is introduced to the breeding flock), ewes should be observed every 4 to 6 hours. Diseases to observe for include signs of pregnancy toxemia, which include refusal to eat grain, opisthotonos, teeth grinding, fine muscle tremors, and coma; signs of hypocalcemia, which include stilted gait, excessive salivation, and recumbency with hind legs extended behind; vaginal prolapse; abortion; mastitis; and rupture of the prepubic tendon. If any of these conditions occurs, prompt treatment should be instituted.
Signs of the first stage of labor include udder enlargement and engorgement with colostrum, relaxation of the pelvic ligaments, and vulvar swelling. The ewe will separate from the flock and begin nesting. If on pasture, she will seek an isolated spot with slight elevation or close to a fence line. Ewes may seek shelter, if it is provided, in order to protect their newborn lambs from inclement weather. Within a paddock, ewes may choose the same location in which to give birth, presumably attracted by the scent of birth fluids. In a pen, ewes may seek a corner or an open claiming pen. She will circle, paw at the straw, and bleat in a low voice. She will stop to smell any uterine or vaginal discharges. As the uterine contractions become stronger and the fetus moves up into the pelvis, she may lie down repeatedly and strain with the head raised.
The second stage of labor generally takes less than an hour from the start of intense straining to the delivery of the lamb. Time to delivery of lambs is approximately 30 minutes or less for a single lamb and up to 2 hours for triplets. Labor in primiparous ewes may take longer. No preference in time of day to deliver has been observed, but if disturbed, the ewe may stop labor for a few minutes until settled again. Normal presentation of the lamb is described as anterior dorsosacral with front limbs extended and preceding the nose by approximately 6 cm (2 to 4 inches). Also normal but associated with greater risk to the safe delivery of the lamb is posterior dorsosacral with hind limbs extended. If delivery is delayed and the umbilical cord is compressed between the lamb and the pelvis of the ewe, the lamb may suffocate before delivery is complete. After delivery of the lamb, the ewe stands, causing the umbilicus to rupture. The ewe turns and begins to nuzzle and lick the lamb to stimulate breathing and to clean it off.
INDUCTION OF PARTURITION
Induction of lambing can be done if the breeding date is known within an accuracy of 3 days—for example, if breeding was synchronized using hormones and only one breeding opportunity occurred. Ewes will respond to an injection of dexamethasone (16 mg given intramuscularly [IM]) or betamethasone (10 to 12 mg IM) after day 137, but it is preferred to wait until day 142 to ensure good fetal viability. Commonly, producers may wait for the first few lambs to be born and then induce the rest of the pregnant ewes. Lambing generally occurs between 36 and 60 hours after induction. Induction is not associated with an increased risk of retained fetal membranes. In instances of vaginal prolapse or pregnancy toxemia, it may be advisable to induce as early as day 137, with the goal of saving the ewe.
MANAGEMENT OF DYSTOCIA
Common Causes of Dystocia
Causes of dystocia may include the following:
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Malpresentation of the lamb
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Maternofetal disproportion
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Poor cervical dilation
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Uterine torsion
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Uterine inertia
Malpresentation of the lamb (or lambs) may manifest in any of various ways: one or both front limbs retained; head retroflexed; true breech presentation, in which the lamb is in the posterior dorsosacral position but the hind legs are flexed forward; dorsopubic or dorsoiliac position; and in the case of multiple births, presence of multiple limbs or heads, or of more than one lamb, in the pelvis at the same time.
Maternofetal disproportion most commonly occurs when ewes that are carrying singles are fed too well in late gestation. Occasionally the ewe may simply have a congenitally small pelvis, or the disproportion may be the result of mating a small-breed ewe and a large-breed ram.
Poor cervical dilation may be due to vaginal prolapse; improper presentation, position, or posture of the lambs; fetal death before stage 1 labor (e.g., from abortion diseases); or possibly damage to the cervix from chronic exposure to phytoestrogens. Ringwomb is the term used to describe incomplete cervical dilation that is unresponsive to manual dilation. The cervix is hard, as it is before stage 1 labor. This condition occurs more frequently in primigravida lambs but may be seen in sheep of any age. Most flocks experience occasional cases of ringwomb, but outbreaks in which up to 15% of ewes are affected have been described.
Uterine torsion occurs occasionally and can be diagnosed on vaginal examination. It may be confused with poor cervical dilation.
Primary uterine inertia may occur if the ewe is ill (e.g., from hypocalcemia or pregnancy toxemia); secondary inertia occurs when the ewe is exhausted after a prolonged labor.
Correction of Dystocia
The practitioner should ensure that the proper tools and protection are available and that the gloves are well lubricated (see Box 91-1). The uterine wall is friable, so only gentle manipulation is advised. A tear in the uterus leads to peritonitis, which is not well tolerated in sheep.
If extensive manipulation is required, use of an epidural anesthetic procedure is advised. The epidural injection generally is performed at the sacrococcygeal space. After the area is clipped and disinfected, a 20-gauge needle is inserted at an angle of 20 degrees to the tail when held horizontally. Lidocaine hydrochloride is then injected at a dose rate of 0.5 mg/kg of body weight (1 ml of 2% lidocaine/40 kg). Additional analgesia may be obtained by combining xylazine with the lidocaine hydrochloride at a dose of 0.07 mg/kg of body weight (0.14 ml of 2% xylazine added to each milliliter of lidocaine hydrochloride). Adult ewes may range in mature body weight from 60 to 80 kg, depending on breed and maturity. This dosage may cause paresis and ataxia of the hindlimbs for up to 8 hours.
With a retained front limb, if the lamb is small, sometimes it may be extracted by gently pulling with the leg still back. With large lambs, however (or small ewes), it is necessary to correct the limb position before delivery is attempted. It generally is necessary to repulse the lamb gently back into the uterus if possible and then, after tracing the limb from the shoulder and elbow, hook the retained leg below the elbow with a finger, bending the carpus and then the fetlock in order to raise the foot over the brim of the pelvis. The practitioner must take care to protect the wall of the uterus from the foot by cupping the foot in the hand. If the fetus cannot be repulsed or if room in the pelvis is insufficient to allow correction of the position, a cesarean section is indicated if the lamb is still alive, or if the lamb is dead, a partial fetotomy is indicated. Viability is determined by checking for the following: suckle reflex, gag reflex, corneal reflex. If none are present, a partial fetotomy is performed by removing the head and neck to increase room to reposition the leg.
With lateral retroflexion of the head, again, an attempt is made to repulse the lamb in order to increase the available space for correction of the head position. A lamb snare around the head and front limbs can be used to help guide the head around. Traction on the lower jaw is avoided unless the lamb is dead, because this usually will result in a fracture to the mandible. If this maneuver is unsuccessful, cesarean section if the lamb is alive or partial fetotomy if the lamb is dead should be considered.
With multiple fetuses, care should be taken to trace limbs and head back to the body and identify which limbs belong to which lambs before repulsion or extraction is attempted.
Maternofetal disproportion may be present concurrently with malposture (e.g., head or limb retroflexion). Once the lamb is in the proper presentation, position, and posture, either soft ropes or the lamb puller can be used to apply gentle traction, ideally to both the front limbs and the head simultaneously. To determine if the lamb can be delivered vaginally, the examiner can assess whether both elbows and the head can be pulled into the pelvis at the same time. Inability to do so with relative ease indicates that vaginal delivery cannot be done safely for the ewe or the fetus. Plenty of lubrication is used to assist extraction. While the lamb is being pulled, after the thorax is clear of the vagina, the lamb is rotated approximately 30 degrees to prevent hip lock.
With poor cervical dilation, the practitioner attempts gentle manual dilation, keeping the hand and arm well lubricated. If after 10 minutes no progress is observed, the problem may be true ringwomb. In this condition, the cervix does not undergo the normal parturient softening. The cervical softening process starts with the prepartal drop in progesterone. This triggers an infiltration of leukocytes, which causes collagen degradation and hence softening. The cause for failure of the cervical softening process is not known. Some success at treatment has been reported with application of an estrogen product or prostaglandin E2 α to the cervical area, or with injection of such agents, and followed in a few hours by oxytocin. The alternative is cesarean section.
With uterine torsion, the practitioner must determine the direction in which the torsion has occurred and then either gently flip the uterus around or hold the fetus and have assistants roll the ewe in the opposite direction of the torsion. In approximately 50% of the cases, poor cervical dilation is present even after detorsion has been accomplished. Cesarean section should be considered in those cases.
If uterine inertia is due to hypocalcemia, the ewe is given parenteral calcium before delivery. This is done by slow intravenous administration of 50 to 100 ml of a commercial calcium borogluconate solution, followed by an additional 50 to 100 ml injected subcutaneously.
After delivery of the lamb primarily responsible for the dystocia, oxytocin (30 to 50 IU) can be given (unless the dystocia is due to uterine inertia). After 10 minutes, the vagina is checked for the presence of additional lambs. If uterine inertia is present, both horns are carefully explored to their ends to locate more lambs.
Cesarean Section
Anesthesia for performing a cesarean section can be obtained using one of the following methods.
A line or inverted "L" block of 2% lidocaine (without epinephrine) can be given on the left flank if a flank laparotomy will be performed, or given ventral midline if that approach will be used.
For the left flank only, paravertebral anesthesia to block the T13, L1, and L2 paravertebral nerves is achieved using the following method: The midpoint of the first lumbar process is confirmed by palpation, and a 6-cm spinal needle is inserted 2.5 to 3.0 cm from the midline along a perpendicular line running from the midpoint of the first lumbar transverse process to the spine and at a depth of 4.0 to 5.0 cm. The needle may need to be directed forward to walk it off the front of the transverse process. After the needle is felt to penetrate the ligament between T13 and L1, 4 to 5 ml of 1% lidocaine hydrochloride is injected to block the 13th thoracic nerve. the needle is retracted and an additional 2 ml is injected to block the dorsal branch of the T13 nerve. The needle is then withdrawn and redirected caudally to block L1 and is walked off the back of the first transverse process. Another 4 to 5 mL is given; then the needle is withdrawn slightly and another 2 ml is injected. To block L2, this technique is repeated but just anterior to the second lumbar process.
An epidural using lidocaine, xylazine, or a combination of both (as described previously) may be used in conjunction with a line or inverted AL block.
Surgical technique is standard. If the fetuses are dead, the uterus should be packed off using sterile drapes before an incision is made. After the first lamb is extracted, both horns should be carefully explored to the tip to detect the presence of more lambs. The practitioner should avoid incising any caruncles because this may result in excessive bleeding. After suturing, oxytocin is administered once and parenteral antibiotics are given for 3 to 5 days.
Fetotomy
Not uncommonly, a dystocia may not be detected until the lambs have died, or in some instances, have become emphysematous. If the lambs cannot be pulled, a fetotomy is preferred to a cesarean section. If the fetus is emphysematous, the uterus also may be compromised and friable. A subcutaneous fetotomy can be performed using a finger knife to avoid vaginal or uterine damage. Again, oxytocin and antibiotics are given at the completion of the procedure.
CARE AND MANAGEMENT OF THE NEONATAL LAMB
Resuscitation of the Newborn Lamb
Lambs normally will begin to breathe within 30 seconds of delivery. Techniques to stimulate the lamb that is slow to breathe include rubbing the head and thorax vigorously with a dry towel, pouring cold water in the ear, and stimulating the sneeze reflex by tickling the nostrils. Swinging the lamb may help extract fluid from the nose but makes it difficult for the lamb to breathe because of centrifugal pressure on the diaphragm. Mouth-to-nose resuscitation should not be done because of the risk of contracting a zoonotic infection from the lamb, such as Chlamydophila abortus or Coxiella burnetii infection. A technique of inflating the lungs that has been used with some success is as follows: A lamb stomach tube is inserted into the esophagus of the lamb. By means of gentle pressure applied with a thumb and forefinger, the esophagus is closed off distal to the end of the tube. The other hand is used to close off the mouth and nostrils. The clinician softly blows once into the tube. With the esophagus closed off, the air will be forced down the trachea into the lungs. The tube is removed after delivery of one breath, and the lamb is reassessed.
Normal Behavior at Birth
Lambs should be standing within 10 to 20 minutes of birth. The normal cleaning behavior of the ewe stimulates them to stand. They are then attracted to the ventral line of the ewe's abdomen and will follow it down to where it meets the udder. The ewe's licking and nudging behavior encourages a suckle reflex. A low udder or an udder covered with wool, or pendulous, misshapen teats, will interfere with successful nursing. The licking also serves to provide olfactory stimulation to aid in maternal recognition of the lamb. This bonding generally occurs in the first hour after birth. It is critical that the ewe have an undisturbed opportunity to bond with her lambs, without the risk of attempts at stealing them by another ewe. Circling behavior is abnormal and indicates that the bonding process is failing. Failure to bond and failure to successfully find the teat are major risk factors for hypothermia/hypoglycemia and septicemia.
The chance of successful bonding will improve if the ewe and lambs are provided with a quiet area, undisturbed by other sheep. Mothering is optimized by confining them in a claiming pen (jug) for 12 to 24 hours. The producer can more easily check the status of the lambs (stomach fill and attitude) and the behavior of the ewe (for signs of rejection) at the time when lambs are most at risk. Claiming pen size should be a minimum of 4 feet by 4 feet; for larger breeds or ewes with multiple lambs, 4 feet by 5 feet is preferred (Fig. 91-1 ). The bottom panels should be spaced close together to prevent the lamb from escaping. Ewes should be provided with fresh water and feed. Heat lamps are optional and should not be used once the lambs are dry.
Plan for a claiming pen.
(Courtesy of Ontario Ministry of Agriculture and Food, Ontario, Canada.)
Passive Immunity
If the ewe is fed correctly in late gestation, is properly vaccinated, and does not have mastitis, she should be able to provide the lamb with colostrum of adequate quantity and quality. Exceptions to this rule of thumb may be observed with maiden ewes and with ewes that have more than two lambs. If the ewe has inadequate colostrum or if the lamb is too weak to nurse properly, then the lamb should be fed colostrum at a rate of 50 ml/kg of body weight within 2 hours of birth and at rate of 200 to 250 ml/kg of body weight over the first 24 hours of life. If the lamb is weak, the colostrum should be administered by stomach tube.
Alternate-Source Colostrum
If the ewe has inadequate colostrum or is considered a risk to pass on specific diseases (e.g., ovine progressive pneumonia [maedi-visna], Johne's disease), colostrum obtained from other animals can be fed. Most ideal is sheep colostrum from a ewe of known health status. Colostrum may be frozen up to 6 months without loss of quality. It should be frozen in 50-ml (approximately 2-ounce) aliquots to facilitate thawing. Rapid thawing with heat (e.g., microwave on high) will denature the immunoglobulins. It is recommended initially to freeze the colostrum in an ice cube tray and then, once it is frozen, to transfer the cubes to a freezer bag labeled with the donor's identification data and the date of freezing. Only first-milk colostrum should be used.
Bovine and caprine colostrum also may be used, but associated risks have been recognized. Ideally, source animals should not be infected with infectious agents that may cause disease in sheep, such as bovine leukosis virus, Mycobacterium avium spp. paratuberculosis, bovine viral diarrhea virus, caprine arthritis encephalitis virus, and Mycoplasma mycoides spp. mycoides. The quality of the colostrum can be improved by vaccinating the donor animals against clostridial diseases.
Anemia due to an unknown factor in cow colostrum has been reported in lambs 1 to 3 weeks of age. This factor appears to increase the rate of red blood cell destruction both in circulation and in the bone marrow of affected lambs. They appear weak and pale. Although many recover without treatment, those severely affected, as indicated by a packed cell volume less than 10%, can be transfused by administering blood (10 ml of whole blood with anticoagulant per kg of body weight given intravenously or by intraperitoneal instillation).
Antibodies obtained from nonhost species may have a shorter half-life. A consequence of this limitation may be a higher risk of infectious diseases such as pneumonia. This also is true of commercial colostrum supplements, which are made from bovine sources. Whey-based products may not contain adequate levels of immunoglobulins. It is not known if serum-derived colostrum supplements provide sufficient protection to lambs.
Umbilical Care
Many opportunistic pathogens may gain entry through the stumps of the umbilical veins or arteries. A solution of 2.5% iodine in an alcohol base should be used to dip the entire navel soon after birth. Solutions containing a higher concentration of iodine may cause chemical burning and inflammation. Products containing glycerin (e.g., commercial teat dips) should not be used, because these prevent drying of the umbilical tissue. Paper disposable cups should be used, and excess dip and the cup discarded afterward.
Vitamin E and Selenium Supplementation
If the flock is located in a selenium-deficient area and the pregnant ewes have not been adequately supplemented, newborn lambs should be injected with a commercial vitamin E plus selenium preparation. The single dose of 0.75 mg of selenium, given by the intramuscular or subcutaneous route, should not be repeated. Toxicity and death have been associated with as little as 1.0 mg of selenium. It is safer and more effective to supplement pregnant ewes at a rate of 0.1 to 0.3 mg of selenium/kg of dry matter (DM) total ration, depending on the natural levels in the feed and governmental restrictions. If the ewe is to be injected with a commercial product rather than supplemented in the feed, 3 mg/45 kg of body weight is given up to every 2 weeks in the last trimester. Only products labeled for use in adult sheep should be used. Although vitamin E does not cross the placental barrier, it should be supplemented to the pregnant ewe at 15 IU/kg DM total ration (1.5 IU = 1.0 mg/dl of α-tocopherol). This will increase vitamin E levels in the colostrum. Lamb rations should contain 20 to 40 IU vitamin E/kg DM total ration. Vitamin A and D injections can be administered to gestating ewes if the ration is deficient.
Identification
Each lamb should be assigned a specific identifier at birth for two reasons: to identify lambs to retain as replacements at a future date and to identify ewe-lamb pairs. Methods include ear tagging, paint branding, and spraying on the back or side with the lamb's identification, the ewe's identification with or without the birth order number and litter size (e.g., 132P-13 would be the firstborn lamb of ewe 132P out of a litter of triplets, and 132P-33 would be the third-born lamb of ewe 132P), or a unique design (e.g., a spiral). The ewe also should be paint-branded at the same time—for example, 132P-3 means that she has 3 lambs at foot. Permanent identification (tag or tattoo) can be given to lambs at birth or at weaning.
Contagious Ecthyma Vaccination
If the flock has significant problems caused by contagious ecthyma virus infection (mastitis, lamb losses, or diminished productivity), then it may be advisable to vaccinate the lambs at birth with a commercial vaccine (if available). The vaccine should not be used in unaffected flocks and need not be used if the disease is only mildly manifested in the flock.
Taildocking and Castration
Taildocking should be routinely performed in all long-tailed breeds within the first 7 days and preferably within the first 24 hours of life, but only after the lamb has received adequate colostrum. Use of either rubber bands or an electric docker is the preferred method. The tail should be docked distal to the end of the tailfold and should be long enough to cover at least the vulva in a ewe lamb. Short docking has been associated with increased risk of rectal prolapse and spinal abscesses.
Castration need not be performed in ram lambs to be marketed before puberty, to take advantage of the improved feed conversion rates of intact rams. If ram lambs are to be castrated, surgery should be performed before 7 days of age if the rubber rings or cut-and-pull technique will be used, and before 90 days of age if the spermatic cord will be crushed. Lambs castrated with rubber rings after 7 days of age should have the cord crushed first in order to destroy the nerves. This appears to reduce the pain associated with that procedure. Lambs born to inadequately vaccinated ewes should be given tetanus antitoxin (250–300 IU administered subcutaneously) at the time of docking or castration. Analgesia at the time of castration or taildocking has been used with variable success. Injection of long-acting local anesthetics proximal to the surgical site may offer temporary relief. Postoperative analgesia may be best provided by administering xylazine before surgery, but animals should be constantly observed until the sedative effects have worn off.
Nutrition of the Nursing Lamb
Peak milk production in ewes occurs approximately 30 days after lambing, and ewe nutrition in the early lactation period should be geared to maximize this production. Ewe's milk provides most of the nutrient requirements for lambs until they reach 30 to 45 days of age. At 10 days of age, lambs will start to consume small amounts of solid feed, but depending on the availability of ewe's milk, intakes of solid feed are low until weaning. To increase intake of solid feed, texturized 16% protein "creep feed" should be available, consisting of mixed grain, pellets containing minerals and medications, and a binding compound, commonly molasses. Feeders should be structured to prevent fecal contamination and wastage of feed. Restricted-access turkey or pig feeders work well for lambs.
Fostering or Artificial Rearing of Lambs
Indications
Indications for fostering or artificial rearing of lambs include the following:
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Dam-related: Death or severe illness may require separation of the lamb from its dam, or the dam may reject the lamb. Other causes may include mastitis or other reason for insufficient milk production, poor udder conformation (too low or teats malformed), and birth of too many lambs to be reared by their dam; or another dam that has lost all her lambs is available as a foster mother.
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Lamb-related: The lamb is unable to nurse its dam effectively because of weakness or congenital deformity.
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Owner-specific: The producer prefers not to have dams rear more than 2 lambs, or not to have dams rear singles, to make nutritional management easier.
Artificial Rearing of the Nursing Lamb (First 4 Weeks)
Most orphan or rejected lambs can be raised on milk replacer until the age of 21 to 28 days, when they can be weaned onto a high-quality creep ration such as described earlier. Lamb milk replacer is higher in fat than calf or kid milk replacer, so the latter should not be used to rear lambs. An example of a good milk replacer is one containing 22% protein from milk sources, 28% fat from animal sources, and 24% lactose. Milk replacer should be fed cold (4° C) and ad libitum from a lamb bar to prevent engorgement and abomasal bloat. In absence of a lamb bar, lambs can be bottle fed from a nipple bottle but should be fed frequently (e.g., 4 times per day). If abomasal bloat losses occur, formaldehyde added to the milk replacer (1 ml/L of milk) will decrease losses.
Foster Rearing
When cross-fostering is used, if at all possible the weakest lambs should be left with the dam, and all fostered lambs should have received adequate colostrum first. Successful fostering of lambs may be accomplished in any of several ways, but ultimately the attitude of the foster dam often determines the success. Attitude may be individual or may be breed determined.
Interventions used to promote successful fostering include the following:
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Manipulating the ewe's detection of scent by skinning the dead lamb and tying the hide to the foster lamb; washing the foster lamb in birth fluids or rubbing it with the fresh placenta; applying various scent blocks to the nares of the ewe.
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Manipulating the ewe's maternal instinct by cervical or vaginal stimulation; removing her own lamb and returning the foster lamb back with her at the same time; "hog-tying" the back leg of the foster lamb to mimic the behavior of a newborn lamb; bringing in a dog to "threaten" the ewe.
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Restraining the ewe so that the lamb can successfully suckle until the ewe accepts the lamb. A stanchion or head gate is the most commonly used device to prevent the ewe from circling. She can still kick, however, so the lamb should be watched to ensure it is able to nurse.
PREVENTION OF PERINATAL LAMB MORBIDITY AND MORTALITY
The perinatal period extends from the first stage of labor. The end of this period is less well defined but this phase can be divided into periods in which specific causes tend to exhibit themselves more commonly. For investigating lamb mortality, losses often are divided into those deaths that occur ante partum, during parturition, and at less than 5 to 24 hours (i.e., until the "mothering-up" process has finished, when bonding has occurred and lamb has ingested colostrum), 5 to 24 hours up to 48 hours (i.e., before acquired infections after birth have caused disease), and beyond 2 days. After 2 days of age, perinatal events can still influence mortality, but effects generally are not observed beyond 2 weeks of age.
Excessive lamb mortality and stillbirth are important limitations on productivity. Stillbirth losses (number of lambs born dead of all lambs born) should not exceed 5%. Lamb mortality levels of greater than 15% before weaning are not uncommon, although with good management, it is possible to keep losses below 5%. Box 91-2 lists possible causes of perinatal lamb mortality.
Investigation of Perinatal Lamb Mortality
A flock health management program should include routine necropsy of all aborted fetuses and stillborn and dead lambs. A simple form can be used to assist in collecting all necessary history and data (Fig. 91-2 ). Findings on gross necropsy can easily be used to diagnose why the lamb died, and to define the management area that is responsible for the loss of the lamb.
A and B, Example of a necropsy form for investigating lamb perinatal mortality.
History
The history should include details of the farm environment and management, as well as ewe and lamb factors. Wet and cold weather can play an important role in lamb losses. Older ewes or ewe lambs may be at greater risk for losing lambs. In excessively thin ewes, risks are greater for production of small lambs, prolongation of labor, and production of inadequate amounts of milk. Litter size, birth weight, and history of dystocia all are important risk factors in lamb mortality. Routine management procedures should be noted, as well as any treatment lambs have received. Notations of previous losses will help to identify problem areas.
Examination of the External Carcass
The examiner should make note of specific abnormalities:
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Atypical condition of coat: abnormal quality and amount of wool, indicating premature birth or congenital infection with border disease virus; meconium staining, indicating stressful birth; adherent placenta, indicating lack of cleaning by the ewe
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Saliva staining around the mouth, indicating endotoxemia (watery mouth)
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Congenital abnormalities (e.g., spider lamb, atresia ani, intersex, cleft palate, arthrogryposis)
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Perineal staining from diarrhea
The footpads are examined to determine whether walking occurred before death, as indicated by some "wear" of the pads; intact footpads signify that the lamb never walked.
Skinning back the carcass, the examiner should note the following:
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Degree of dehydration, keeping in mind that length of time since death and freezing may confound accurate observation
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Subcutaneous edema (regional or generalized); ascites, anasarca, or swollen head due to dystocia
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Bilateral swelling on the neck, which may be an enlarged thyroid, suggesting goiter due to iodine deficiency
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Umbilicus, to determine whether the umbilicus is blunt and arteries are empty, evidence that the lamb died before or during the birth process; is tapered and contains blood, evidence that the lamb survived the birth process; or is tapered and contains an organized adherent clot, evidence that the lamb survived the birth process by several hours. Hyperemia, fibrin, and purulent material in the umbilical region indicate omphalophlebitis.
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The skeletal muscles, which should be checked for evidence of white muscle disease
The skin should be removed from the limbs and the subcutaneous tissues examined for hemorrhages, which indicate that the lamb was hypothermic before death.
For internal examination, the lamb carcass should be opened with its right side down and the organs examined in situ. The following should be noted:
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Evidence of pleural or peritoneal fibrin, indicating a septic condition before death. Swabs of this fluid should be submitted for culture. If an agent associated with abortion is suspected, abomasal contents and thoracic fluid or heart blood should be collected using sterile needles and syringes (see Chapter 90).
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Blood in the peritoneal cavity, which may be from a ruptured liver, kidney, or mesenteric or umbilical vessel and suggests trauma occurring in utero, during parturition, or post partum, depending on other findings.
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Blood-tinged fluid in the peritoneal or pleural cavity, which may indicate that the lamb died in utero 1 or 2 days before delivery.
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The amount of brown fat around the kidney and heart, which should be evaluated. Serous atrophy suggests that the lamb was hypoglycemic before death. Heart fat is depleted first, then kidney fat.
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Aeration of the lungs, which can be assessed quickly by dropping a piece of lung tissue in a jar of water to assess buoyancy, and evidence of pneumonia. Total atelectasis of the lungs indicates that the lamb never breathed. The trachea and bronchi should be opened to examine for aspiration pneumonia (the owner may have incorrectly passed a stomach tube).
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The tongue, diaphragm, and heart should be sectioned and examined for evidence of white muscle disease. The heart should be checked for congenital defects.
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The abomasum should be examined for type and quantity of content. An empty abomasum or an abomasum that contains dirt or grass, along with the finding of serous atrophy of fat, suggests that the lamb survived at least 5 hours but never nursed. Detection of milkfat in the mesenteric lymphatics suggests that several hours have passed since feeding.
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The skull and the brain, particularly the atlanto-occipital region, should be examined for hemorrhages, both subdural and throughout the brain, indicating the possibility of birth trauma.
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The joints all should be opened to look for evidence of septic arthritis.
By using the information gathered on gross necropsy (Fig. 91-3 ), the death of the lamb can be classified as follows (Fig. 91-4 ):
Algorithm for classification of lamb perinatal mortality.
Classification of timing of death in lambs and common causes of mortality.
Prepartum—early.
The lamb appears obviously premature, with decreased or absent wool coat. This should be considered an abortion and investigated as such (see Chapter 90).
Prepartum—late.
The lamb appears to be term but was delivered stillborn, with no evidence of birth trauma. Although the lamb's death may have been from delayed parturition due to uterine inertia, it is advisable to investigate the death as an abortion.
Parturient.
Evidence of birth trauma is present, and the lungs are atelectatic.
Postparturient, early.
Death occurred after birth but most often before 5 hours of age—up to 24 hours. Brown fat stores are evident, and the lungs are partially or fully inflated. The lamb may have been weak when born because of infection with abortion agents, may have succumbed to birth-related injuries, with or without evidence of hypothermia, or may have been primarily hypothermic.
Late postparturient, older than 5 to 24 hours.
After 5 hours of age, lambs start to deplete their brown fat stores if they do not receive adequate nourishment (colostrum). Mismothering, inadequate colostrum supply, and weakness due to low birth weight or birth trauma will predispose the lamb to starvation (hypoglycemia). Up to 48 hours of age, death often is related to primary hypoglycemia with secondary hypothermia.
Neonatal, older than 48 hours.
Although death after 48 hours may still be due to hypothermia or hypoglycemia secondary to birth trauma, mismothering, and other causes, after this time infectious diseases also can occur.
Recognition and Treatment of Weak Lambs
It is important to instruct the producer on how to recognize a sick lamb and how to apply appropriate nursing care. Hypothermia and hypoglycemia are the most common causes of lamb mortality; if recognized early, both are responsive to treatment. Affected lambs initially are hunched up and empty-appearing. If the problems are not detected early, these lambs will become recumbent. If in sternal position, the lamb may rise but appears depressed and slow to respond. Eventually, the lamb is laterally recumbent and comatose.
Figure 91-5 presents an algorithm for treatment for a lamb suspected of suffering from hypothermia or hypoglycemia. The client should be instructed in proper technique for tube feeding, with specific measures to avoid aspiration pneumonia: The client sits with the lamb on his or her lap, holding the lamb's head and neck gently in the nondominant arm. The tube is introduced slowly into the mouth and gently pushed toward the back of the throat. If the lamb sucks on the tube, a swallowing reflex is encouraged. Once the tube has been swallowed, the client can feel it pass down the lamb's neck in the esophagus. This maneuver should be practiced several times until the client can recognize the feel of the rubber end passing the fingers. If the tube enters the trachea, it cannot be felt externally. Premeasurement of the tube will help the client to determine if the tube has reached the abomasum. If the lamb coughs, the tube is withdrawn and another attempt is made. Colostrum can be fed by syringe or squeeze bottle. The dose of 50 ml/kg of body weight should be fed slowly over 5 to 10 minutes, so that the abomasum does not overfill, leading to regurgitation. The client is instructed to kink the tube before withdrawal to prevent aspiration of milk.
Algorithm for treatment of hypothermia and hypoglycemia in neonatal lambs.
Many ways to warm a lamb have been described. Immersion in warm water is the most rapid but requires that the client hold the lamb while in water and then dry it immediately, to avoid chilling from evaporation. Placement in a warming box in which the lamb lies on a grate that allows warm air to circulate around it generally works the best (Fig. 91-6 ). A household hair dryer works well for this purpose. Air temperature should not exceed 41° C. A warming pad will accomplish the same thing if the lamb also is covered with a blanket and turned frequently. Least efficient is use of a heat lamp, which offers only radiant heat to the exposed part of the lamb.
Warming box for reviving hypothermic lambs.
Lambs older than 5 hours of age require an energy source before warming. Failure to provide energy will result in central nervous system damage from hypoglycemia. If no suckle reflex is present, the lamb should have 20% dextrose administered into the intraperitoneal cavity. This procedure begins with drawing up 20 ml of 50% dextrose into a 60-ml syringe and adding to it 30 ml of hot, boiled, clean water. The resultant solution should be at body temperature. Instillation into the peritoneal cavity is accomplished by hanging the lamb vertically and injecting just off midline distal to the umbilicus, using a sterile 20-gauge needle and administering 10 ml/kg of body weight. After administration, the lamb can be warmed.
Once a lamb has received treatment for hypothermia/hypoglycemia, it and its dam should be identified for more intense observation. Factors that put lambs at risk for hypothermia and hypoglycemia include the following:
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Poor maternal nutrition during gestation (reduces the number of cotyledons and placental weight; brown fat stores [perirenal and pericardiac] in fetus; lamb birth weight; mammary development and subsequent milk production; colostrum quality and quantity)
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Low birth weight (<3 kg), which is highly correlated with poor brown fat stores
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High birth weight (>5 kg), which is highly correlated with dystocia
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Trauma or hypoxia due to dystocia or prolonged birth, which may be evidenced by meconium staining
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Premature birth (<142 days' gestation)
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Mismothering due to inexperience (e.g., ewe lamb), illness, stealing by another ewe, lack of availability of claiming area, claiming of only the firstborn lamb
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Insufficient milk available as a result of mastitis, poor late-gestation nutrition, maedi-visna (ovine progressive pneumonia) or other illness, low body condition score, poor udder or teat conformation, wool-covered udder
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Poor environmental conditions at birth of the lambs, such as a cold temperature (<13° C if fleece is wet), drafty conditions, and dirty or wet bedding or ground
Two exceptionally high-risk periods have been recognized:
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Birth to 5 hours, when the lamb is wet. Losses at this time are due primarily to hypothermia or are secondary to birth trauma.
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5 hours to 7 days, when hypothermia most often is secondary to hypoglycemia. Weakness after 48 hours of age also may be complicated by diseases stemming from inadequate colostrum intake.
CONTROL OF IMPORTANT DISEASES OF NEONATAL LAMBS
Entropion
Entropion usually is apparent within the first 2 weeks of age and manifests as ocular discharge, blepharospasm, corneal edema, and corneal ulceration due to irritation from inverted eyelids, usually the lower lid. Correction should be done immediately and may involve one of the following procedures: Mild cases may be resolved by manually everting the lid several times a day for a few days. Moderately severe cases may be resolved by an injection of penicillin into the palpebral conjunctiva. The resulting bleb should be sufficient to roll the eyelid out. Occasionally the procedure needs to be repeated in 5 to 7 days. Other, surgical-type methods include pinching a small amount of tissue into two wound clips placed parallel to the lower lid, crushing a fold of skin with hemostats parallel to the lower lid, and cutting a length of skin from below the lower lid and suturing it. With all of these latter methods, care must be taken to apprehend sufficient skin to allow proper eversion of the eyelid. Some evidence indicates that this is a heritable condition, so lambs with entropion should not be selected as replacements, particularly rams.
Diseases Due to Clostridium spp.
Tetanus, pulpy kidney, and enterotoxemia are diseases of neonatal lambs that can be easily prevented through a routine vaccination program with a multivalent vaccine. The vaccine should contain immunizing antigens to Clostridium tetani, Clostridium perfringens types C and D, Clostridium septicum, Clostridium novyi type B, and Clostridium chauvoei. Every replacement lamb should receive a primary series after 10 to 12 weeks of age and a booster at least every 12 months. To ensure optimal colostral protection to their lambs, the booster should be administered to pregnant ewes no later than 2 weeks before the first expected lambing date of their breeding group.
Coccidiosis
Clinical and subclinical coccidiosis is a major cause of poor growth in lambs. Management practices that will reduce environmental exposure to coccidial oocysts include use of properly designed feeders that do not allow for fecal contamination of the feed; provision of a clean bedding pack or slatted floors for nursing and growing lambs; and a raised water source. Thorough disinfection before lambing may reduce the level of coccidia in the environment, but adult ewes and then lambs quickly recontaminate the pens. It often is necessary to also use a drug that controls coccidia. Table 91-2 lists the commonly used preventive treatments for coccidiosis. Feed additives should be added to free-choice pelleted or texturized lamb rations to ensure adequate intakes. A prescription often is required for addition of these coccidiostats because of the variability among countries in licensing these drugs for use in sheep. Commercial cattle feeds or supplements with coccidiostats included should not be used because of the high risk of copper toxicity.
Table 91-2
Drugs Commonly Used to Control Coccidiosis in Lambs
| Commercial Name | Active Ingredient | Dose (BW/day) | Mode of Delivery | Comments |
|---|---|---|---|---|
| Various | Sulfadimidine-sulfamethazine | 25–140 mg/kg | In water; 4 days on, 3 off, then repeat | Higher dose is used for treatment (4 days); toxic if treatment is prolonged; lower dose is used for prevention/control (long term) |
| Sulfaquinoxaline | 13 mg/kg | 0.015% solution for 3–5 days | ||
| Amprol* | Amprolium | 20 mg/kg | 5 days as a drench; 21 days in feed or water | Resistance reported; toxic at higher doses |
| Rumensin | Monensin | 1 mg/kg | 11 mg/kg in free-choice–fed or 22 mg/kg in limit-fed animals in complete feed for 6 to 8 weeks | Toxic if mixed incompletely or incorrectly |
| Bovatec | Lasalocid | 1 mg/kg | 36 mg/kg in free-choice–fed animals for 6 to 8 weeks | Moderate toxicity |
| Deccox 6% Premix | Decoquinate | 0.5–1.0 mg/kg | 1.5 kg of premix/ton of complete feed, or calculate according to known intakes for minimum of 75 days | Not toxic; can be added to mineral premix to prevent disease in pastured weaned lambs |
| Clinicox 0.5% | Diclazuril | 1 mg/kg | Either 1 dose or 2 treatments 14 days apart at 3–4 weeks of age | Disease may occur despite treatment in highly challenging environmental conditions |
Neonatal Diarrhea
Lambs are susceptible to the same infectious agents as those identified for calves. Generally, enteropathogenic Escherichia coli causes disease at 2 to 7 days of age. Rotavirus and coronavirus may cause diarrhea from 2 days to 3 weeks of age. Cryptosporidia most often affect lambs after 2 weeks of age. Salmonella spp. and Giardia are less common causes. If the flock is experiencing high morbidity from neonatal diarrhea during the lambing period, ewes that are still pregnant should be moved to a clean area for lambing. People managing the sick lambs should not handle newborn lambs without changing and washing their clothes in disinfectant soap. Vaccination of pregnant ewes with a bovine E. coli scour vaccine has been done, but a preferred approach is first to attempt to break the cycle by focusing on cleaning and disinfection of the lambing and lamb-rearing environments.
Pneumonia
The most common cause of pneumonia in neonatal lambs is Mannheimia hemolytica. Most often the strain involved is A2, with A1 being the most common strain in bovine pneumonia. Other agents that may be involved are Mycoplasma ovipneumoniae and Pasteurella trehalosi. Various viruses may play a role in increasing suscepti-bility of lambs to these disease agents. Environmental conditions, however, appear to be more important in determining the incidence of pneumonia in young lambs. Stocking density, humidity, diurnal or nocturnal temperature fluctuations, extreme heat and cold, frequency of air changes, ammonia levels, and dust all increase the stress on the respiratory system. In outbreaks of pneumonia, metaphylaxis has been used with success. Drugs that are licensed for use in sheep for pneumonia include short-acting oxytetracycline, tilmicosin (Micotil* ), and ceftiofur (Excenel† ). Other antimicrobials that may be effective but are not licensed for sheep include long-acting oxytetracycline and florfenicol (Nuflor‡ ).
Generally, antimicrobial resistance is not a reason for treatment failure. Most often the reason is failure to detect sick animals soon enough or not treating for long enough. It is important to train the client to observe nursing lambs carefully for depression. This should be done outside the pen so as to not arouse the lambs until identified for further clinical examination. Necropsy of dead lambs is a good way to determine the reason for treatment failure. A vaccine against M. hemolytica infection in sheep is not available in North America.
Footnotes
*Provided for clients with an established relationship with the practitioner.
*Provel, Elanco, Greenfield, IN.
†Pfizer, New York, NY.
‡Shering-Plough, Kenilworth, NJ.
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